Worldwide more than 400 million people are chronically infected with HBV and are, thus, at increased risk of developing serious liver disease, such as chronic hepatitis, cirrhosis, liver failure and hepatocellular carcinoma (HCC) resulting in an estimated 600,000 deaths each year.
The natural evolution of chronic HBV infection includes four consecutive phases: (1) early ‘immunotolerant’ phase, high levels of virus replication and minimal liver inflammation; (2) immune reactive phase, significant hepatic inflammation and elevated serum aminotransferases; with some patients progressing to (3) ‘non-replicative’ phase, seroconversion to anti-HBe; undetectable or low level of viremia (below 2000 IU/ml by PCR-based assays); resolution of hepatic inflammation; and (4) HBeAg-negative chronic hepatitis B, due to the emergence of specific viral mutations, which prevent the production of HBeAg but do not hamper virus replication. This form of chronic hepatitis B (CHB) is characterized by fluctuating serum HBV DNA and serum aminostransferases (ALT and AST) levels, and progressive liver disease. It is important to note that CHB may present either as HBeAg-positive or HBeAg-negative CHB. Longitudinal studies of patients with CHB indicate that the 5-year cumulative incidence of developing cirrhosis ranges from 8 to 20%. The 5-year cumulative incidence of hepatic decompensation is approximately 20%. The worldwide incidence of HCC has increased and presently constitutes the fifth most common cancer. The annual incidence of HBV-related HCC is high, ranging from 2-5% when cirrhosis is established.
The primary goal of treatment for HBV is to permanently suppress HBV replication and improve liver disease. Clinically important short-term goals are to achieve HBeAg-seroconversion, normalization of serum ALT and AST, resolution of liver inflammation and to prevent hepatic decompensation. The ultimate goal of treatment is to achieve durable response to prevent development of cirrhosis, liver cancer and prolong survival. HBV infection cannot be eradicated completely due to persistence of a particular form of viral covalently closed circular DNA (ccc HBV DNA) in the nuclei of infected hepatocytes. However, treatment-induced clearance of serum HBsAg is a marker of termination of chronic HBV infection and has been associated with the best long-term outcome.
The current standard methods of treatment for HBV include interferon or thymosin a1-based immunotherapies and the suppression of viral production by inhibition of the HBV polymerase. HBV polymerase inhibitors are effective in reducing viral production but have little to no effect in rapidly reducing HBsAg or can slowly reduce HBsAg with long term treatment in a limited number of patients (as is the case with tenofovir disoproxil fumarate). Interferon based immunotherapy can achieve a reduction of both viral production and early removal of HBsAg from the blood but only in a small percentage of treated subjects. The generally accepted role of HBsAg in the blood is to sequester anti-HBsAg antibodies and allow infectious viral particles to escape immune detection which is likely one of the reasons why HBV infection remains a chronic condition. In addition HBsAg, HBeAg and HBcAg all have immuno-inhibitory properties and the persistence of these viral proteins in the blood of patients following the administration of any of the currently available treatments for HBV is likely having a significant impact in preventing patients from achieving immunological control of their HBV infection.
Although the three primary HBV proteins (HBsAg, HBeAg and HBcAg) all have immunoinhibitory properties, HBsAg comprises the overwhelming majority of HBV protein in the circulation of HBV infected subjects. Additionally, while the removal (via seroconversion) of HBeAg or reductions in serum viremia are not correlated with the development of sustained control of HBV infection off treatment, the removal of serum HBsAg from the blood (and seroconversion) in HBV infection is a well-recognized prognostic indicator of antiviral response on treatment which will lead to control of HBV infection off treatment (although this only occurs in a small fraction of patients receiving immunotherapy). Thus, while reduction of all three major HBV proteins (HBsAg, HBeAg and HBcAg) may result in the optimal removal of inhibitory effect, the removal of HBsAg alone is likely sufficient in and of itself to remove the bulk of the viral inhibition of immune function in subjects with HBV infection.
Therefore, in the absence of any current treatment regimen which can restore immunological control of HBV in a large proportion of patients, there is a need for an effective treatment against HBV infection which can inhibit viral replication as well as restore immunological control in the majority of patients. Accordingly, there is a need in the art for alternative therapies and combination therapies for subjects infected with HBV and/or having an HBV-associated disease.